A $12-$ha catchment has pre$-$ and post$-$development times of concentration of $2\mathrm{.}5$ h and $1\mathrm{.}5$ h respectively, and the pre$-$ and post$-$development runoff coefficient are estimated as $0\mathrm{.}3$ and $0\mathrm{.}6.$ respectively. The IDG function is given by

$\backslash [$

i$=\backslash$frac$\{7836\}\{37\mathrm{.}7+0\mathrm{.}803$ t$\}\backslash$mathrm$\{$~mm$\}/\backslash$mathrm$\{$h$\}$

$\backslash ]$

Where i is the rainfall intensity in $\backslash (\backslash$mathrm$\{$mm$\}/\backslash$mathrm$\{$h$\}\backslash )$ and t is the duration in minutes. Use the modified rational method to estimate the required storage so that the post$-$development peak runoff rate is equal to the pre$-$development peak runoff rate. What is the ratio of the storage volume to the runoff volume?